If you grabbed a microphone and conducted a poll of random people on the street and asked them, “What makes the world go around?” you would get varied responses. Many would say “love” or “information” while a few would say “energy.” Well, if we exclude the abstracts, those few would be right. In today’s high-tech world, there is nothing tangible that drives our daily activities more than energy. This can be further refined to electrical energy, more commonly referred to as power. The ability to distribute adequate power to the systems that utilize it reliably is the greatest challenge that we face.
Electric vehicles (EVs), and to a lesser degree hybrid electric vehicles (HEVs), face the same challenge. This issue can be viewed from two perspectives: the availability of external sources or charging stations and the distribution of power to the automotive electronics systems that comprise the vehicle. For engineers and designers of automotive electronics PCBs, devices and systems, the former is assumed while the latter is a significant design concern. For example, material selection depends on the amount of power distributed throughout your board. Let’s take a look at the EV systems and how you can design automotive electronics to optimize power distribution.
Automobile Electronics for Electric Vehicles
Traditional automobiles are based on a 12V DC energy supply system. As EV and HEV technology has evolved, this has proven to be inadequate. Today, HEVs are typically based on a 48V DC energy supply while EVs may be as high as 400V DC. This means that the vehicle battery is 48V or 400V, although individual electronics devices may operate at other lower voltage levels. Aside from the fact that electric vehicles require higher power to operate, there are other advantages to using a higher voltage level for these systems.
The transmission of DC power over conductors comes with high losses as heat is dissipated into the surrounding environment. This is a significant concern for copper due to its high heat transfer rate. Additionally, higher voltages are needed to supply high-power devices and components.
To supply power to all automotive electronic and electrical systems, electric vehicles utilize staged power conversion. This process consists of DC-DC conversion and DC-AC conversion or inversion.
This conversion stage reduces the voltage level from 48V or higher (depending on the battery). Devices or systems that require DC supply may be directly connected to this converter stage, although voltage or current regulators may be used to maintain a constant supply. Typically, automotive electronics control circuitry are driven from the DC source.
DC-AC conversion is performed primarily to drive the AC motor. The motor, in turn, drives the transmission, which drives the wheel rotation.
Electric vehicles, similar to non-electric vehicles, contain a large number of other components and systems that perform various operations, including lighting, monitoring, major functions and accessory control. A standard car has approximately 30,000 components. HEVs contain a similar number of components as they require all the components for combustion and electric operation, while EVs have significantly less.
Design Tips for Electric Vehicle Automotive Electronics
Due to the complexity and number of different systems, managing the power distribution to automotive electronics is challenging. For EVs and HEVs, the usage of more power and higher voltages and currents presents additional concerns for designing PCBs for automotive electronics. However, a few simple tips can be used as a guide to achieve well-designed high-power boards.
Tip 1: Choose board materials that can withstand high temperatures
High power usually means high current for PCBs. Therefore, you should select materials rated to withstand higher temperatures like Teflon laminate and Polytetrafluoroethylene (PTFE) or Polyimide substrates.
Tip 2: Space high power components apart
High power components can quickly raise the temperature of your board, and excessive heat in a small area can damage your board. The best option is to space these components as far apart as possible to optimize heat distribution on your board.
Tip 3: Make good use of thermals
To help dissipate heat as fast as possible, it is a good idea to utilize signal vias as thermal vias. These may be directly underneath SMDs or nearby for components with surface pins. To help optimize thermal usage, you should apply good thermal resistance management. For high power components, it is also a good idea to employ adequately designed heatsinks.
Tip 4: Follow good grounding design rules
Good grounding design is also essential to maintain isolation between different signal types and expedite heat dissipation. This includes properly placing a sufficient number of ground planes within your PCB stackup.
Tip 5: Use larger copper weights
Current flow can be controlled by using larger copper weights, such as 2oz instead of the standard 1oz. This can be an effective means of managing trace resistance.
The above design tips include guidelines that should be a part of your PCB thermal DFM. Instituting these tips in synchronization with the capabilities of your contract manufacturer (CM) will undoubtedly aid in designing your automotive electronics PCBs to manage the distribution of the high power that these boards utilize.